Field of the Invention
Embodiments of the present invention relate generally to the field of semiconductor processing. More specifically, embodiments of the invention are directed to methods and apparatus for enhancing the cooling of substrates which have been heated through radiative processes.
Background of the Related Art
A number of applications involve thermal processing of semiconductor and other materials, which require precise measurement and control of the temperature of the material. For instance, processing of a semiconductor substrate requires precise measurement and control of the temperature over a wide range of temperatures. One example of such processing is rapid thermal processing (RTP), which is used for a number of fabrication processes, including rapid thermal annealing (RTA), rapid thermal cleaning (RTC), rapid thermal chemical vapor deposition (RTCVD), rapid thermal oxidation (RTO), and rapid thermal nitridation (RTN). In the particular application of CMOS gate dielectric formation by RTO or RTN, thickness, growth temperature, and uniformity of the gate dielectrics are parameters that influence the overall device performance and fabrication yield. Some of these processes require variations in temperature across the substrate of less than a few degrees Celsius.
According to the International Technology Roadmap for Semiconductors, transistor SDE junction depths of 11 nm are required for the next nodes. Rapid Thermal Processing Spike Anneal is reaching a limitation as the time at temperature is limited to around one second with current technology. The millisecond anneal is a potential solution, but is difficult to integrate unless in combination with some RTP. As an immediate solution, RTP could be extended if the time at temperature could be reduced further.
It is desirable for temperatures to be as uniform as practicable in a substrate during thermal processing of the substrate. Additionally, it is desirable to decrease the amount of time required to cool the substrate after certain processes, e.g. spike anneal, are completed. In practice, the edge region of a substrate is thermally affected by the periphery of the RTP chamber more than are other regions of the substrate, leading to chronic temperature non-uniformities residing in the edge region. Standard control algorithms are designed to respond to radial temperature non-uniformities once detected. For very short processes, such as spike anneal processes, the control algorithm may not be able to compensate quickly enough, resulting in temperature non-uniformities near the edge of the substrate. Further, because the current design of RTP chambers is geared toward radial temperature non-uniformity on a circular substrate, this method of temperature control is unable to correct non-radial temperature non-uniformities, for example a “cold spot” that is not symmetrically centered on the substrate.
Thus, there is still a need for methods and apparatus for controlling the rapid thermal processing of a substrate that may be used for a wide range of substrates that enhance the cooling rate of substrates.